1. Field of the Invention
The present invention relates to an apparatus for controlling an amount of fluid for heavy construction equipment, which can constantly supply an amount of hydraulic fluid to an actuator and prevent fluid from being fed back from the actuator in occasions that a load pressure on the actuator mounted in heavy construction equipment such as excavators and a pressure of a hydraulic pump vary.
2. Description of Prior Art
FIG. 1 is a view for showing a hydraulic circuit of a conventional apparatus for controlling an amount of fluid for heavy construction equipment.
As shown in FIG. 1, the conventional apparatus for controlling an amount of fluid for heavy construction equipment includes a hydraulic pump P connected to an engine, an actuator 300 connected to the hydraulic pump P and driven upon supplying hydraulic fluid, a control valve 100 mounted to a parallel hydraulic path 103 between the hydraulic pump P and the actuator 300 and for controlling starts, stops, and direction switchings of the actuator 300, and fluid amount control valves 400, 400A, and 400B mounted in paths between ports 101 and 102 on outlets of the control valve 100 and the actuator 300 and for restricting an amount of fluid supplied to the actuator 300 and controlling a driving speed thereof.
A reference number 105 not described in the drawing denotes a central bypass path, and 106 a relief valve for draining hydraulic fluid into a hydraulic oil tank T when a load over a pressure set in the hydraulic circuit is developed.
Accordingly, as a pilot signal pressure Pi based on a manipulation of a joy stick not shown is applied to the right end of the control valve 100 to switch an inner spool to the left direction on the drawing of FIG. 1, hydraulic fluid discharged from the hydraulic pump P is supplied to a large chamber 302 of the actuator by way of the parallel path 103 and the position-switched control valve 100, and, at the same time, hydraulic fluid fed back from a small chamber 301 of the actuator 300 is drained to the hydraulic oil tank T via a check valve 405B, causing the actuator 300 to drive.
At this time, in case of restricting the amount of fluid in order to control a driving speed of the actuator 300 according to a work condition, the fluid amount control valve 400A can control the amount of fluid flowing in the large chamber 302 based on a pressure difference with a spring valve 404A set according to a pressure difference of inlet and outlet paths 402A and 403A of a spool 402 due to the extent of the opening of a throttle valve 401A.
However, the fluid amount control apparatus as stated above requires separate blocks to install the hydraulic amount control valve 400 in the hydraulic paths between the ports 101 and 102 at the outlets of the control valve 100 and the actuator 300, causing problems increasing the costs due to the increase of the number of parts, interfering among parts on a layout when designing, and making its use impossible in a place of narrow space.
Further, as mentioned above, the fluid amount control valve 400 does not have a check function for the case that a load pressure on the side of the actuator is higher than a discharge pressure on the side of the hydraulic pump P, causing a problem separately installing the check valve 104 in the parallel path 103 at the side of the inlet of the control valve 100.
FIG. 2 is a view for showing a hydraulic circuit for a conventional apparatus for controlling an amount of fluid.
As shown in FIG. 2, the fluid amount control apparatus has a hydraulic pump P, actuators A, B, and C connected to the hydraulic pump and driven upon hydraulic fluid supplies, and direction switching valves D, E, and F installed in hydraulic paths between the hydraulic pump P and the actuators A, B, and C and for controlling the flow directions of the hydraulic fluids supplied to the actuators A, B, and C.
At this time, the direction switching valve E includes a pump path 500 connected to the actuator B, load paths 503 and 504 having load ports 501 and 502 communicated with the actuator B, a transfer path 505 branched from the pump path 500 and connected to the load paths 503 and 504, a control valve 511 mounted in a central bypass path 510 and for controlling hydraulic fluid supplied to the actuator B, a seat valve 512 mounted to be opened and shut between the pump path 500 and the control valve 511, and a pilot spool valve 513 mounted between the seat valve 512 and the control valve 511, enabling to restrict an amount of hydraulic fluid supplied to variable throttle valves 515 and 516 of the control valve 511 through the pump path 500 and the transfer path 505 from the hydraulic pump P and to control an amount of hydraulic fluid flowing in the load paths 503 and 504 of the actuator B.
At this time, the transfer path 505 has a path 506 communicated with the pump path 500, a pair of paths 507 and 508 positioned on both sides of the path 506, and an annular path 509 connecting the pair of paths 507 and 508 and the path 506.
Accordingly, as a pilot signal pressure due to an manipulation of a driver is applied to a control valve 514 of the direction switching valve D, hydraulic fluid discharged from the hydraulic pump P is supplied to the actuator A via the position-switched control valve 514 to drive the actuator A, thereby proportionally controlling the amount of the hydraulic fluid supplied to the actuator B via the control valve 511 switched owing to the application of the pilot signal pressure.
However, since the pilot spool valve 513 maintains an initial open state all the time, in case that load pressures occurring on the load paths 503 and 504 of the actuator B are higher than a pressure of the hydraulic fluid discharged from the hydraulic pump P, a feedback flow occurs through the seat valve 512 and then a set working pressure is not supplied to the actuator B to make impossible its controls, causing a problem bringing out a safety incident.
In taking it into account, a feedback prevention check valve is installed in a seat valve not shown, but it has a loose response to the feedback, causing a problem deteriorating the reliability of equipment and raising the manufacture cost due to the increase the number of parts.
Further, an amount of hydraulic fluid supplied to the actuator B according to a load pressure of the actuator B and a discharge pressure from the hydraulic pump P varies, leading to a problem developing a safety incident.
It is an object of the present invention to provide an apparatus for controlling an amount of fluid for heavy construction equipment, which can prevent layout interferences when designing and be used in a narrow space due to a compact structure that a fluid amount control valve controlling a driving speed of an actuator is installed inside a control valve controlling a flow direction of hydraulic fluid supplied to the actuator.
It is another object of the present invention to provide an apparatus for controlling an amount of fluid for heavy construction equipment, which can enhance the durability of parts by reducing hunting and shock phenomena due to variations of a load pressure of an actuator and a pressure of a hydraulic pump.
It is yet another object of the present invention to provide an apparatus for controlling an amount of fluid for heavy construction equipment, which can enhance a response property by carrying out a function of a check valve when a load pressure of a work device is higher than a discharge pressure of a hydraulic pump.
In order to achieve the above objects, an apparatus for controlling an amount of fluid for heavy construction equipment according to a preferred embodiment of the present invention, in an apparatus for controlling an amount of fluid for heavy construction equipment having a hydraulic pump, an actuator connected to the hydraulic pump and driven upon hydraulic fluid supplies, and a control valve installed in a parallel fluid path between the hydraulic pump and the actuator and for controlling starts, stops, and direction switchings of the actuator, comprises a logic check valve mounted to be opened and shut between an inlet-side path of the control valve and the parallel path, and a logic control valve for opening and shutting an inlet-side path communicated with the parallel path and an outlet-side path connected to a pressure chamber of the logic check valve upon switching based on a set elastic force of a valve spring and a pressure in a path on a side of the actuator connected to one side of the pressure chamber with respect to a pressure in an inlet-side path connected to the other side of the pressure chamber.
According to a preferred embodiment, an orifice is installed in the outlet-side path connecting the logic check valve and the logic control valve.
Further, a piston is installed in the pressure chamber of the logic check valve and an orifice is installed in a path passing through the piston.
Further, a check valve is installed in a path connecting the logic check valve and the inlet-side path, and an orifice is installed in a branched path before and after the check valve.
Further, an orifice is installed in the path connecting the inlet-side path of the logic control valve and the pressure chamber of the logic check valve.
Further, a variable orifice is installed in an inlet-side path of a spool of the logic control valve.
Further, the logic check valve further includes a controllable throttle for varying an opening area with respect to an inlet path from the parallel path based on displacements of a valve seat of the logic check valve.